Automatic vehicle identification (AVI) is known in the art.
A common use for AVI is to electronically monitor and charge vehicles entering or moving on toll highways by means of an interrogator and transponder. The interrogator is a transmitter/receiver device owned by the highway operator that communicates with transponders that are installed within the vehicles. One or more of such interrogators are installed at the entrance or at specific locations along sections of the highway. Upon receipt of a valid interrogation signal, the vehicle transponder responds by transmitting the identity of the car (or any other unique signal enabling the identification of the car) to the interrogator. Upon receipt and processing of the transponder signal, the highway operator can charge the car owner for using the highway.
The interrogators and transponders usually operate by means of electromagnetic signals, but other types of communication means, for example, optical, ultrasonic, etc may also be used. Most commonly, the interrogators and transponders operate by means of RF signals, and therefore the transponder is sometimes referred to as “RF ID”. Furthermore, specific protocol standards, as well as proprietary protocols, have been developed for such interrogator-transponders communication, for example ASTM V6 and CALTRANS Title 21.
FIG. 1, to which reference is now made, shows a typical AVI transponder 1 together with an optional hanging device 2. Transponder 1 is generally attached to the internal surface of the front vehicle window (windshield), or to a location close to the window by means of some attachment device. For example, the device may be attached to the window by means of hanging device 2. Hanging device 2 typically has a double sided adhesive (not shown) at its rear surface, and hangers 3a and 3b at the front. Hanging device 2 is generally attached to the windshield at a location which at most minimally obstructs a driver's view; for example, behind the front mirror.
Typically, transponder 1 is an electronic card or a small circuit which is mounted within a closed, sometimes molded casing. Transponder 1 typically comprises means to provide an electronic beep which may be used to occasionally alert the driver as the car passes an interrogator at the beginning/end of a section of the highway.
Such transponders and interrogators are also commonly used in other applications. For example, transponders 1 can also be used as is, or with minimal modification, to facilitate weigh in motion (WIM) applications, access control and management, traffic management probes and other location based services.